Sir Henry Cecil, who has died aged 70, was among the outstanding flat-racing
trainers of the late 20th century.

In his heyday between 1976 and 1993, Cecil was 10 times champion trainer, and over the course of his career won 25 Classics, 14 of them with fillies. He took the Oaks eight times and the 1,000 Guineas six times, and won four Epsom Derbies, three 2,000 Guineas and four St Legers. His stable was associated with some of the greatest jockeys of the age, among them Joe Mercer, Lester Piggott, Steve Cauthen and Kieren Fallon.

Then, after a period of decline, in the winter of his career Cecil enjoyed a spectacular renaissance as the trainer of the unbeaten Frankel, arguably one of the greatest racehorses ever seen. Having won the 2011 2,000 Guineas by six lengths, Frankel went on to take a string of big races, among them the St James’s Palace Stakes, Queen Elizabeth II Stakes and (by 11 lengths) the 2012 Queen Anne Stakes. Frankel won the 2012 Sussex Stakes at Goodwood (at odds of 1-20) and followed this with a facile victory in the Juddmonte International at York, the first time he had raced over more than a mile.

Frankel’s final race was at Ascot, in October 2012, when he won the Champion Stakes, over 10 furlongs on testing ground, by one and three quarter lengths from Cirrus Des Aigles. It was his 14th win on the bounce.

While some of his fellow trainers could appear somewhat bucolic, the tall, slim and soigné Cecil might have been beamed to the racecourse straight from Curzon Street or from some exotic foreign boulevard. As he chatted to his owners in the parade ring, he would adopt an elegant slouch, head tilted to one side, a cigarette dangling from his hand.

But this public air of nonchalance concealed a steely ambition to succeed, an immense capacity for hard work and a relentless attention to detail. He never bet. In truth, Cecil was a shy and private man — albeit one of considerable personal charm — whose passion outside his work was gardening; and although born to a life of privilege, he endured perhaps more than his share of suffering and reversal.

Henry Richard Amherst Cecil was born on January 11 1943, 10 minutes in advance of his identical twin David. A fortnight earlier his father, also Henry, the younger brother of Lord Amherst of Hackney, had been killed in North Africa while serving with the Parachute Regiment (he was recommended for a posthumous Victoria Cross).

Henry’s mother, Rohays, daughter of Major-General Sir James Burnett, Bt, was left with four young sons, and in 1944 married the trainer Capt Cecil Boyd-Rochfort, when he was 56 and still regarded as the most eligible bachelor in Newmarket. She was soon running a house whose staff included a butler and footmen; one of the servants was an Italian who had played the accordion for Mussolini.

At his prep school, Sunningdale, Henry remained rooted in the bottom form, and as goalkeeper for the school’s football team once let in 14 goals in a match against Ludgrove. He and David became the first Sunningdale pupils to fail the examination for Eton and were sent instead to Canford School, Dorset, where Henry garnered nine O-levels.

During his teens he rode out for his stepfather and enjoyed attending race meetings. On leaving school he and David joined the staff of Lord Derby’s Woodland Stud at Newmarket and in their spare time raced greyhounds at Bury St Edmunds. Henry later worked at a stud in the United States before attending Cirencester Agricultural College, where he and his brother spent most of their time racing and drinking. While David then became a bloodstock agent, Henry became assistant trainer to his stepfather.

He was thus joining what had been one of the most successful stables of the era. Capt Boyd-Rochfort had won 13 Classics and had trained for King George VI and later for the Queen. By now the best days of the stable, Freemason Lodge, were past, but the young Cecil was able to absorb his stepfather’s accumulated knowledge and his methods. He began courting Julie Murless, daughter of Boyd-Rochfort’s great rival Noel Murless, who trained at Warren Place in Newmarket, and they married in 1966. On the morning of the wedding Cecil — who at this stage of his life was a heavy drinker — was suffering from “one of the roughest hangovers I have ever had”.

Boyd-Rochfort retired in 1968, and the next year Cecil set up on his own, first at Freemason Lodge. It was a dispiriting start, and after a while he gave up attending the races “because I was tired of hearing people say, 'Don’t back that. It’s Cecil’s. He couldn’t train ivy up a wall.’ ” It was mid-May before he sent out his first winner, Celestial Cloud, at Ripon. Then, in July, he won his first group race when Wolver Hollow took the Eclipse at Sandown; and after his two-year-old Approval also won a group race he finished eighth in the list of the season’s winning trainers.

The following season Henry and Julie Cecil rented the Marriott Stables, and over the next few years built on that early success. His first classic winner came in 1975, when Bolkonski won the 2,000 Guineas.

At the end of 1976 Sir Noel Murless retired, and Cecil bought his training establishment, Warren Place, a mile outside Newmarket, formerly the principal residence in England of the Maharajah of Baroda. Over the next 13 years Cecil was to win 12 more Classic races.

Things began to go wrong for Cecil in 1989, when he began an affair with Natalie Payne, who worked for a bloodstock agency, leading to the break-up of his marriage. Many in the Newmarket racing community sided with Julie Cecil, and when she set up as a trainer in her own right some of the staff at Warren Place left to join her.

In 1995 Cecil suffered a professional reversal when one of his principal owners, Sheikh Mohammed Al Maktoum, withdrew his horses from Warren Place. Although the Sheikh had sound reasons — he was in the process of establishing Godolphin, his own breeding and training operation — it was also suggested that he had been dismayed by what he saw as “interference” in the Warren Place set-up by Natalie (now Cecil’s wife).

Classic victories were to continue, however, with Bosra Sham lifting the 1,000 Guineas and Lady Carla winning the Oaks in 1996. Cecil won two more classics in 1997 and a further three in 1999, including a fourth Derby victory, with Oath.

Thereafter his fortunes — both professional and personal — took a turn for the worse. In 2000 his twin brother David died of cancer. His second marriage fractured after the press reported that his wife had had an affair with an unnamed jockey. Cecil dispensed with the services of his stable jockey, Kieren Fallon, who later won a £300,000 out-of-court settlement for unfair dismissal.

Warren Place went into a relative decline. Cecil reflected in 2007: “I had some virus in the yard that took three or four years to get rid of… Then, within a year or two, I lost some of the owner-breeders I used to train for, Howard de Walden, Jim Joel, Louis Freedman and others. I’d always trained for owner-breeders, and owner-breeders had become a dying race. I’d always been very lucky to have some of Sheikh Mohammed’s horses. Then he went under his own flag. When you’re not having winners you go out of fashion, and I began to go out of fashion. People said I’d lost interest because of my personal life. That was never true, but in the end I did get quite demoralised and depressed. I didn’t have the horses.”

He reduced his staff, rented out part of his yard and put money into his Cliff Stud, in Yorkshire, where he also kept sheep and raised organic beef.

Some owners — notably Prince Khaled Abdullah and the Niarchos family — remained loyal, and gradually winners began to flow once more from Warren Place. In 2007 he had his first Classic winner in seven years when Light Shift won the Oaks at Epsom.

In the previous year Cecil had been diagnosed with stomach cancer, and with so many achievements behind him he had adopted a reflective mood. “I’m quite happy with a smaller string,” he said in 2007. “It gives me time to go and watch cricket if I feel like it, to help do the garden, to spend time with my son [by Natalie] Jake. With 70 or 80 nice horses I’d like to think I can be competitive.”

He won the 1,000 Guineas with One in a Million (1979), Fairy Footsteps (1981), Oh So Sharp (1985), Bosra Sham (1996), Sleepytime (1997) and Wince (1999); the 2,000 Guineas with Bolkonski (1975), Wollow (1976) and Frankel (2011); and the St Leger with Light Cavalry (1980), Oh So Sharp (1985), Reference Point (1987) and Michelozzo (1989).

As well as his remarkable haul of English Classics, in Ireland Cecil won a 1,000 Guineas, two Derbies and three Oaks. He was a master at producing winners at Royal Ascot, sending out more than 70 winners there over the course of his career.

Among his other well-known horses were Indian Skimmer (winner of the 1987 Prix de Diane); Ardross (twice winner of the Ascot Gold Cup and the Yorkshire Cup); Kris; Le Moss; and Twice Over, winner of the Champion Stakes (2009) and the Eclipse (2010). In 2009 he won the Breeders’ Cup for fillies and mares with Midday.

He was knighted in 2011.

At Warren Place Cecil created a fine private rose garden which occupied much of his leisure time. Another passion was shopping for clothes; at one time his extensive wardrobe included dozens of pairs of Gucci shoes. He and Julie Cecil once owned a boutique in Newmarket called The Clothes Horse.

In 1983 he published an autobiography, On the Level.

With his first wife, Henry Cecil had a son and a daughter. The marriage was dissolved in 1990, and he married secondly, in 1992, Natalie Payne, with whom he had a son. That marriage was dissolved in 2002.

In 2008 he married his former secretary, Jane McKeown, sister of the former jockey Richard Guest, winner of the Grand National on Red Marauder in 2001.